Default value gets set to 'NULL' when Allow NULL value is changed to true

[dstoyanoff]

Preflight Checklist

• I have completed all Troubleshooting Steps.
• I'm on the latest version of Directus.
• There's no other issue that already describes my problem.

Describe the Bug

When a field's Allow NULL value setting is updated from false to true, the column's default value gets set to stringified 'NULL'

To Reproduce

• Create a new collection
• create 2 fields
  • field1 - Allow NULL value = true
  • field2 - Allow NULL value = false
• inspect the database - everything is ok.
• update field2 to have Allow NULL value = true
• inspect the database - field2's default value got updated to NULL::character varying

What version of Directus are you using?

v9.0.0-rc.90

What version of Node.js are you using?

v16.5.0

What database are you using?

Postgres 12

What browser are you using?

Edge

What operating system are you using?

macOS

How are you deploying Directus?

Docker

[rijkvanzanten]

I think this might be a quirk in Postgres actually!

Before:

SQL:

ALTER TABLE articles
	ALTER COLUMN title SET NOT NULL,
	ALTER COLUMN title SET DEFAULT NULL;

After:

[rijkvanzanten]

It still seems to behave as expected though:

When inserting directly in SQL, omitting the value for title:

ERROR: null value in column "title" of relation "articles" violates not-null constraint

In Directus:

[rijkvanzanten]

I think this is just a confusing quirk in Postgres on how it displays a default value NULL for string type columns that aren't nullable. No idea why it does that tho!